NEW YORK (Reuters Health) - More than one in five middle-school aged children with behavioral or emotional problems has recently engaged in sexting, according to a new study.

What's more, researchers found those who reported sexting in the past six months were four to seven times more likely to also engage in other sexual behaviors, compared to adolescents who said they didn't sext.

"We know early adolescents are using mobile phones and all forms of technology more and more and we know that early adolescence is a time when people become engaged in sexual activity," Christopher Houck said. "So how those two connect is an important area of study."

Houck is the study's lead author and a staff psychologist at Rhode Island Hospital's Bradley Hasbro Children's Research Center in Providence.

"Sexting" refers to sending nude or seminude images or sexually explicit messages over an electronic device, such as a mobile phone.

Previous research has found that about one in four teens admits to sexting, but the new study is among the first to estimate how many younger adolescents send sexually explicit images or messages.

Houck cautioned, however, that the findings are based on youths who were determined to have behavioral and emotional problems. They may not apply to all middle-school aged children.

The 420 participants, who were between 12 and 14 years old, were recruited from five urban public middle schools in Rhode Island between 2009 and 2012.

The results are based on an initial questionnaire the participants took as part of a larger study that is attempting to reduce risky behaviors among adolescents with behavioral or emotional problems.

Overall, 17 percent of the participants said they had sent a sexually explicit text message in the past six months. Another 5 percent reported sending both sexually explicit text messages and nude or seminude photos, according to findings published Monday in the journal Pediatrics.

Adolescents who said they were further along in puberty and those who had trouble processing their emotions were most likely to report sexting.

"It could be that for kids who have trouble with emotional processing that it's a little bit easier to sext somebody than to say face-to-face, 'Hey, I like you' and see what that response is," Houck said.

The researchers also found that participants who reported any type of sexting were between four and seven times more likely to engage in other sexual behaviors, compared to those who didn't sext.

Those other behaviors included making out, touching genitals and having vaginal or oral sex.

Adolescents who reported sending sexually explicit images in addition to text messages were the most likely to engage in those other behaviors, according to the researchers.

Youths who reported sexting were also more likely to report intending to have sex, Houck said.

"I think it adds to the growing literature on this that the line between offline and online behaviors is becoming increasingly blurred," Jeff Temple, who was not involved with the new research, told Reuters Health of the study.

Temple is director of behavioral health and research in the Department of Obstetrics and Gynecology at the University of Texas Medical Branch in Galveston.

He said this and similar studies reinforce calls for parents and guardians to have ongoing conversations with adolescents about sexual behaviors, including sexting.

"It should go hand in hand with a talk about healthy relationships and sexual behavior," Temple said. "It's just part of the new portfolio of adolescence these days."